Projection device and projection-type video display device

ABSTRACT

Provided are a projection device and a projection-type video display device capable of displaying a plurality of videos, allowing speckles to be inconspicuous, and miniaturizing an optical system. A projection device includes an optical element including light diffusion elements capable of diffusing light, an irradiation device configured to irradiate the optical element with illumination light beams, each illumination light beam scanning the corresponding light diffusion element, spatial light modulators, each spatial light modulator being illuminated with illumination light beam which is incident from the irradiation device to each light diffusion element to be diffused, and projection optical systems, each projection optical system projecting modulation image obtained on each spatial light modulator on corresponding screen. The illumination light beam, which is incident to each position of each light diffusion element to be diffused, overlappedly illuminates on corresponding spatial light modulator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/568,204, filed Dec. 12, 2014, which in turn is a continuation of U.S.application Ser. No. 13/821,082, filed Mar. 6, 2013, now U.S. Pat. No.8,950,871, which in turn is a National Stage of PCT/JP2011/070514, filedSep. 8, 2011, the entireties of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a projection device and aprojection-type video display device displaying a plurality of videos byusing a coherent light beam, and more particularly, to a projectiondevice and a projection-type video display device capable of allowingoccurrence of speckles to be inconspicuous.

BACKGROUND OF THE INVENTION

A projection-type video display device, including a screen and aprojection device which projects a video image on the screen, has beenwidely used. In a typical projection-type video display device, atwo-dimensional image as a basic image is generated by using a spatiallight modulator such as a liquid crystal micro display or a DMD (digitalmicromirror device), and the two-dimensional image is magnified andprojected on a screen by using a projection optical system, so that avideo is displayed on the screen.

As the projection device, various types including a commercializedproduct called an “optical type projector” have been proposed. In ageneral optical type projector, the spatial light modulator such as aliquid crystal display is illuminated by using an illumination deviceincluding a white light source such as a high pressure mercury lamp, andan obtained modulation image is magnified and projected on the screen byusing lenses. For example, Patent Literature 1 listed below discloses atechnique where a white light beam generated by a supper-high pressuremercury lamp is divided into three primary color components R, G, and Bby a dichiroic mirror, the light beams are guided to spatial lightmodulators corresponding to the primary colors, generated modulationimages corresponding to the primary colors are combined by a crossdichiroic prism to be projected on the screen.

As an application of the projection device and the projection-type videodisplay device, a projection device which projects video imagecorresponding to each screen on a plurality of the screens is known. Inaddition, a technique where signals representing different images can beoutput from one information processing terminal is also known, and videois displayed on a plurality of the screens by using the technique andthe projection device.

A plurality of the projection devices are needed in order to project thevideo light beam corresponding to each screen on a plurality of thescreens. At this time, although a plurality of the spatial lightmodulators and a plurality of the projection optical systems are needed,it has been considered that the projection device can be miniaturized bycommonly using the illumination device illuminating the spatial lightmodulators.

However, the illumination device of the related art uses a high pressuremercury lamp, an LED, or the like as a light source to spread a lightbeam of the light source and transmit the light beam. In theillumination device of the related art, since the light beam is spread,there is a loss in light intensity, and there is a problem in that anoptical system becomes large.

Further, high intensity discharge lamp such as a high pressure mercurylamp has a relatively short lifecycle, and in the case where the lamp isused for an optical type projector or the like, the lamp needs to befrequently replaced. In addition, since a relatively large opticalsystem such as a dichiroic mirror is needed in order to extract thelight beams of the primary color components, there is a problem in thatthe size of the whole apparatus is increased as described above.

In order to cope with this problem, a type using a coherent light sourcesuch as a laser is also proposed. For example, a semiconductor laserwhich is widely used in industries has a very long lifecycle incomparison with the high intensity discharge lamp such as a highpressure mercury lamp. In addition, since the laser source is a lightsource capable of generating light having a single wavelength, aspectroscopic apparatus such as a dichiroic mirror is unnecessary, sothat there is an advantage in that the whole apparatus can beminiaturized. Further, since the diameter of the light beam of the lasercan be easily controlled, a loss of light may not easily occur.

On the other hand, in the type using the coherent light source such as alaser source, there is another problem in that speckles occur. Thespeckle is a punctate pattern which occurs when the coherent light beamsuch as a laser beam is irradiated on a scattering plane. If the speckleoccurs on the screen, it is observed as punctate luminance irregularity(brightness irregularity), so that it becomes a factor of exertingphysiologically bad influence on the observer. The reason why thespeckles occur in the case of using the coherent light beam is that thecoherent light beams reflected from portions of the scatteringreflecting plane such as a screen have very high coherency, and thespeckles are generated through interference therebetween. For example,in Non Patent Literature 1 listed below, theoretical review of theoccurrence of speckles is made in detail.

In the type of using the coherent light source, since there is anintrinsic problem in that the speckles occur, techniques for suppressingthe occurrence of speckles have been proposed. For example, PatentLiterature 2 listed below discloses a technique where a scattering plateis irradiated with a laser beam, an obtained scattered light beam isguided to a spatial light modulator, and the scattering plate is drivento rotate by a motor, so that speckles are reduced.

CITATION LIST

-   Patent Literature 1: JP 2004-264512 A-   Patent Literature 2: JP 6-208089 A-   Non Patent Literature 1: Speckle Phenomena in Optics, Joseph W.    Goodman, Roberts & Co., 2006

SUMMARY OF INVENTION Problem to be Solved by the Invention

As described above, with respect to the projection device and theprojection-type video display device using the coherent light source,the techniques for reducing speckles which have been proposed up to nowmay not effectively and sufficiently suppress the speckles. For example,in the method disclosed in Patent Literature 2 described above, sincethe laser beams irradiated on the scattering plate are scattered, aportion of the laser beams are lost without contribution to videodisplay. In addition, the scattering plate needs to be rotated in orderto reduce the speckles, the mechanical rotation mechanism becomes arelatively large apparatus, and the power consumption is increased.Moreover, although the scattering plate is rotated, the position of theoptical axis of the illumination light beam is not changed, so that thespeckles occurring due to the diffusion on the screen may not besufficiently suppressed.

The inventors have researched based on the problems describedhereinbefore, so that the inventors contrived a projection device and aprojection-type video display device displaying a plurality of videos byusing a coherent light beam, which are capable of allowing speckles tobe inconspicuous and miniaturizing optical systems. In other words, thepresent invention is to provide a projection device and projection-typevideo display device which can display a plurality of videos and whichare capable of allowing speckles to be inconspicuous and miniaturizingoptical systems.

Means for Solving the Problem

According to the present invention, there is provided a first projectiondevice displaying video corresponding to each screen on a plurality ofthe screens, including:

an optical element including a plurality of light diffusion elementscapable of diffusing light;

an irradiation device configured to irradiate the optical element with aplurality of illumination light beams, each illumination light beamscanning the corresponding light diffusion element;

spatial light modulators, each spatial light modulator being illuminatedwith illumination light beam which is incident from the irradiationdevice to each light diffusion element to be diffused; and

projection optical systems, each projection optical system projectingmodulation image obtained on each spatial light modulator oncorresponding screen,

wherein the illumination light beam, which is incident to each positionof each light diffusion element to be diffused, overlappedly illuminateson corresponding spatial light modulator, and

wherein the irradiation device includes:

a light source configured to generate a coherent light beam;

a light division unit configured to divide the coherent light beam fromthe light source to generate a plurality of divided light beams;

optical fibers, each optical fiber transmitting each divided light beamfrom the light division unit; and

a scan device configured to change propagation direction of each dividedlight beam transmitted by the optical fibers and allow each dividedlight beam as each illumination light beam to scan the correspondinglight diffusion element.

According to the present invention, there is provided a secondprojection device displaying video corresponding to each screen on aplurality of the screens, including:

an optical element including a plurality of light diffusion elementscapable of reproducing images of scattering plates in correspondingilluminated regions;

an irradiation device configured to irradiate the optical element with aplurality of illumination light beams, each illumination light beamscanning the corresponding light diffusion element;

spatial light modulators, each spatial light modulator disposed toposition which overlap each illuminated region; and

projection optical systems, each projection optical system projectingmodulation image obtained on each spatial light modulator oncorresponding screen,

wherein the illumination light beam incident from the irradiation deviceto each position of each light diffusion element is allowed to reproducethe image of the scattering plate corresponding to each light diffusionelement in the corresponding illuminated region, and

wherein the irradiation device includes:

a light source configured to generate a coherent light beam;

a light division unit configured to divide the coherent light beam fromthe light source to generate a plurality of divided light beams;

optical fibers, each optical fiber transmitting each divided light beamfrom the light division unit; and

a scan device configured to change propagation direction of each dividedlight beam transmitted by the optical fibers and allow each dividedlight beam as each illumination light beam to scan the correspondinglight diffusion element.

In the first or second projection device of the present invention, thescan device may include mirrors which reflect the divided light beamsand change propagation direction of each divided light beam by changinga direction of each mirror.

In the first or second projection device of the present invention, thescan device may change propagation direction of each divided light beamby changing direction of emitting end of each optical fiber.

In the first or second projection device of the present invention, eachdivided light beam may be irradiated to one point of the correspondingmirror, each divided light beam reflected by the one point of the mirrorconstitutes a diverging flux from the corresponding one point, and eachdiverging flux is incident on the corresponding light diffusion element.

In the first or second projection device of the present invention, eachdivided light beam may be irradiated to one point of the correspondingmirror, and each divided light beam reflected by the one point of themirror may constitute a diverging flux from the corresponding one point,and the projection device may further include a parallel lightgeneration unit which propagates each light beam constituting eachdiverging flux in a certain direction to generate parallel light fluxand allow each parallel light flux to be incident on the correspondinglight diffusion element.

According to the present invention, there is provided a third projectiondevice displaying video corresponding to each screen on a plurality ofthe screens, including:

an optical element including a plurality of light diffusion elementscapable of diffusing light;

an irradiation device configured to irradiate the optical element with aplurality of illumination light beams, each illumination light beamscanning the corresponding light diffusion element;

spatial light modulators, each spatial light modulator being illuminatedwith illumination light beam which is incident from the irradiationdevice to each light diffusion element to be diffused; and

projection optical systems, each projection optical system projectingmodulation image obtained on each spatial light modulator oncorresponding screen,

wherein the illumination light beam, which is incident to each positionof each light diffusion element to be diffused, overlappedly illuminateson corresponding spatial light modulator, and

wherein the irradiation device includes:

a light source configured to generate a coherent light beam;

a light division unit configured to divide the coherent light beam fromthe light source to generate a plurality of divided light beams;

a scan device configured to change propagation direction of each dividedlight beam from the light division unit; and

optical fibers, each optical fiber transmitting each divided light beamincident from the scan device and irradiating the optical element witheach divided light beam as each illumination light beam, and

wherein the scan device allows each illumination light beam to scan thecorresponding light diffusion element.

According to the present invention, there is provided a fourthprojection device displaying video corresponding to each screen on aplurality of the screens, including:

an optical element including a plurality of light diffusion elementscapable of reproducing images of scattering plates in correspondingilluminated regions;

an irradiation device configured to irradiate the optical element with aplurality of illumination light beams, each illumination light beamscanning the corresponding light diffusion element;

spatial light modulators, each spatial light modulator disposed toposition which overlap each illuminated region; and

projection optical systems, each projection optical system projectingmodulation image obtained on each spatial light modulator oncorresponding screen,

wherein the illumination light beam incident from the irradiation deviceto each position of each light diffusion element is allowed to reproducethe image of the scattering plate corresponding to each light diffusionelement in the corresponding illuminated region, and

wherein the irradiation device includes:

a light source configured to generate a coherent light beam;

a light division unit configured to divide the coherent light beam fromthe light source to generate a plurality of divided light beams;

a scan device configured to change propagation direction of each dividedlight beam from the light division unit; and

optical fibers, each optical fiber transmitting each divided light beamincident from the scan device and irradiating the optical element witheach divided light beam as each illumination light beam, and

wherein the scan device allows each illumination light beam to scan thecorresponding light diffusion element.

In the third or fourth projection device of the present invention, eachillumination light beam may constitute a diverging flux from an emittingend of the corresponding optical fiber, and each diverging flux may beincident on the corresponding light diffusion element.

According to the present invention, there is provided a fifth projectiondevice displaying video corresponding to each screen on a plurality ofthe screens, including:

an optical element including a plurality of light diffusion elementscapable of diffusing light;

an irradiation device configured to irradiate the optical element with aplurality of illumination light beams, each illumination light beamscanning the corresponding light diffusion element;

spatial light modulators, each spatial light modulator being illuminatedwith illumination light beam which is incident from the irradiationdevice to each light diffusion element to be diffused; and

projection optical systems, each projection optical system projectingmodulation image obtained on each spatial light modulator oncorresponding screen,

wherein the illumination light beam, which is incident to each positionof each light diffusion element to be diffused, overlappedly illuminateson corresponding spatial light modulator, and

wherein the irradiation device includes:

a light source configured to generate a coherent light beam;

a light division unit configured to divide the coherent light beam fromthe light source to generate a plurality of divided light beams;

mirror optical systems, each mirror optical system transmitting eachdivided light beam from the light division unit; and

a scan device configured to change propagation direction of each dividedlight beam incident from the mirror optical systems and allow eachdivided light beam as each illumination light beam to scan thecorresponding light diffusion element.

According to the present invention, there is provided a sixth projectiondevice displaying video corresponding to each screen on a plurality ofthe screens, including:

an optical element including a plurality of light diffusion elementscapable of reproducing images of scattering plates in correspondingilluminated regions;

an irradiation device configured to irradiate the optical element with aplurality of illumination light beams, each illumination light beamscanning the corresponding light diffusion element;

spatial light modulators, each spatial light modulator disposed toposition which overlap each illuminated region; and

projection optical systems, each projection optical system projectingmodulation image obtained on each spatial light modulator oncorresponding screen,

wherein the illumination light beam incident from the irradiation deviceto each position of each light diffusion element is allowed to reproducethe image of the scattering plate corresponding to each light diffusionelement in the corresponding illuminated region, and

wherein the irradiation device includes:

a light source configured to generate a coherent light beam;

a light division unit configured to divide the coherent light beam fromthe light source to generate a plurality of divided light beams;

mirror optical systems, each mirror optical system transmitting eachdivided light beam from the light division unit; and

a scan device configured to change propagation direction of each dividedlight beam incident from the mirror optical systems and allow eachdivided light beam as each illumination light beam to scan thecorresponding light diffusion element.

In the fifth or sixth projection device of the present invention, thescan device may include mirrors which reflect the divided light beamsand change propagation direction of each divided light beam by changinga direction of each mirror, and each divided light beam may beirradiated to one point of the corresponding mirror, each divided lightbeam reflected by the one point of the mirror may constitute a divergingflux from the corresponding one point, and each diverging flux may beincident on the corresponding light diffusion element.

In the fifth or sixth projection device of the present invention, thescan device may include mirrors which reflect the divided light beamsand change propagation direction of each divided light beam by changinga direction of each mirror, each divided light beam may be irradiated toone point of the corresponding mirror, each divided light beam reflectedby the one point of the mirror may constitute a diverging flux from thecorresponding one point, and the projection device may further include aparallel light generation unit which propagates each light beamconstituting each diverging flux in a certain direction to generateparallel light flux and allow each parallel light flux to be incident onthe corresponding light diffusion element.

According to the present invention, there is provided a seventhprojection device displaying video corresponding to each screen on aplurality of the screens, including:

an optical element including a plurality of light diffusion elementscapable of diffusing light;

an irradiation device configured to irradiate the optical element with aplurality of illumination light beams, each illumination light beamscanning the corresponding light diffusion element;

spatial light modulators, each spatial light modulator being illuminatedwith illumination light beam which is incident from the irradiationdevice to each light diffusion element to be diffused; and

projection optical systems, each projection optical system projectingmodulation image obtained on each spatial light modulator oncorresponding screen,

wherein the illumination light beam, which is incident to each positionof each light diffusion element to be diffused, overlappedly illuminateson corresponding spatial light modulator, and

wherein the irradiation device includes:

a light source configured to generate a coherent light beam;

a scan device configured to change a propagation direction of thecoherent light beam from the light source;

a collimation optical system configured to collimate the coherent lightbeam from the scan device;

a light division unit configured to divide the collimated coherent lightbeam to generate a plurality of divided light beams; and

mirror optical systems, each mirror optical system transmitting eachdivided light beam from the light division unit and irradiating theoptical element with each divided light beam as each illumination lightbeam, and

wherein the scan device allows each illumination light beam to scan thecorresponding light diffusion element.

According to the present invention, there is provided an eighthprojection device displaying video corresponding to each screen on aplurality of the screens, including:

an optical element including a plurality of light diffusion elementscapable of reproducing images of scattering plates in correspondingilluminated regions;

an irradiation device configured to irradiate the optical element with aplurality of illumination light beams, each illumination light beamscanning the corresponding light diffusion element;

spatial light modulators, each spatial light modulator disposed toposition which overlap each illuminated region; and

projection optical systems, each projection optical system projectingmodulation image obtained on each spatial light modulator oncorresponding screen,

wherein the illumination light beam incident from the irradiation deviceto each position of each light diffusion element is allowed to reproducethe image of the scattering plate corresponding to each light diffusionelement in the corresponding illuminated region, and

wherein the irradiation device includes:

a light source configured to generate a coherent light beam;

a scan device configured to change a propagation direction of thecoherent light beam from the light source;

a collimation optical system configured to collimate the coherent lightbeam from the scan device;

a light division unit configured to divide the collimated coherent lightbeam to generate a plurality of divided light beams; and

mirror optical systems, each mirror optical system transmitting eachdivided light beam from the light division unit and irradiating theoptical element with each divided light beam as each illumination lightbeam, and

wherein the scan device allows each illumination light beam to scan thecorresponding light diffusion element.

In the seventh or eighth projection device of the present invention,each illumination light beam may constitute a parallel light flux, andeach parallel light flux may be incident on the corresponding lightdiffusion element.

According to the present invention, there is provided a projection-typevideo display device including:

any one of the first to eighth projection device; and

screens on which modulation images obtained on the spatial lightmodulators are projected.

In any one of the first to eighth projection device of the presentinvention, the light diffusion element may be a hologram recordingmedium.

In any one of the first to eighth projection device of the presentinvention, the light diffusion element may be a lens array.

Advantageous Effects of Invention

According to the present invention, it is possible to display aplurality of videos, to allow speckles to be inconspicuous, and tominiaturize an optical system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating configurations of anillumination device, a projection device, and a projection-type videodisplay device according to a specific example of a basic embodiment asa diagram illustrating the basic embodiment among embodiments of thepresent invention.

FIG. 2 is a diagram illustrating the illumination device illustrated inFIG. 1.

FIG. 3 is a diagram illustrating an exposing method for manufacturing ahologram recording medium constituting an optical element of theillumination device illustrated in FIG. 2.

FIG. 4 is a diagram illustrating functions of the hologram recordingmedium manufactured by the exposing method illustrated in FIG. 3.

FIG. 5 is a perspective diagram illustrating functions of theillumination device illustrated in FIG. 1.

FIG. 6 is a schematic diagram illustrating configurations of anillumination device, a projection device, and a projection-type videodisplay device according to a first modified example of the basicembodiment as a diagram corresponding to FIG. 1.

FIG. 7 is a schematic diagram illustrating configurations of anillumination device, a projection device, and a projection-type videodisplay device according to a second modified example of the basicembodiment as a diagram corresponding to FIG. 1.

FIG. 8 is a schematic diagram illustrating configurations of anillumination device, a projection device, and a projection-type videodisplay device according to a third modified example of the basicembodiment as a diagram corresponding to FIG. 1.

FIG. 9 is a perspective diagram illustrating a modified example of theirradiation device and functions thereof as a diagram corresponding toFIG. 5.

FIG. 10 is a perspective diagram illustrating another modified exampleof the irradiation device and functions thereof as a diagramcorresponding to FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings. Note that, in the drawings attached to thespecification, for the better understanding and the convenience ofillumination, reduction scales, aspect ratios, and the like areexaggerated differently from those of real objects.

A projection device and a projection-type video display device accordingto the embodiments of the present invention have a basic configurationcapable of effectively preventing speckles from occurring.

In the description hereinafter, first, a configuration which is capableof allowing speckles to be inconspicuous and displaying a plurality ofvideos, and functions and effects which can be obtained based on theconfiguration will be described as a basic embodiment with reference toa projection-type video display device including a projection deviceillustrated in FIGS. 1 to 5. After that, a modified embodiment will bedescribed.

Basic Embodiment Configuration of Basic Embodiment

First, a configuration of a projection-type video display device whichincludes an illumination device and a projection device projectingcoherent light beams and which is capable of allowing speckles to beinconspicuous to display a plurality of videos will be described mainlywith reference to FIGS. 1 to 5.

The projection-type video display device 10 illustrated in FIG. 1includes three screens 15-1, 15-2, and 15-3 and a projection device 20which projects video light beams including corresponding coherent lightbeams to the screens 15-1, 15-2, and 15-3. The projection device 20includes an illumination device 40 which simultaneously illuminatesthree illuminated regions LZ1, LZ2, and LZ3 located on a virtual planewith the coherent light beams, three spatial light modulators 30-1,30-2, and 30-3 which are disposed at positions overlapping theilluminated regions LZ1 to LZ3 and are illuminated with the coherentlight beams by the illumination device 40, and three projection opticalsystems 25-1, 25-2, and 25-3 which project each modulation imageobtained on each of the spatial light modulators 30-1 to 30-3 to thecorresponding screen 15-1 to 15-3 respectively.

For example, a transmission-type liquid crystal micro display may beused as the spatial light modulators 30-1 to 30-3. In this case, each ofthe spatial light modulators 30-1 to 30-3 which are illuminated in aplanar shape by the illumination device 40 selectively transmits thecoherent light beam for each pixel, so that each of the modulationimages is formed on the screen of each display constituting each of thespatial light modulators 30-1 to 30-3. The modulation images (videolight beams) obtained in this manner are changed in magnification andprojected to the corresponding screens 15-1 to 15-3 by the projectionoptical systems 25-1 to 25-3. Therefore, the modulation images aredisplayed on the screens 15-1 to 15-3 with changed magnification(generally, enlargement), so that an observer can observe the threeimages.

Note that, a reflection-type micro display may be used as the spatiallight modulators 30-1 to 30-3. In this case, the modulation images areformed by reflected light beams in the spatial light modulators 30-1 to30-3, and the plane irradiated with the coherent light beams illuminatedfrom the illumination device 40 to the spatial light modulators 30-1 to30-3 and the plane of the video light beams constituting the modulationimages progressing from the spatial light modulators 30-1 to 30-3 arethe same plane. In the case where the reflected light beams are used, aMEMS element such as a DMD (Digital Micromirror Device) may be used asthe spatial light modulators 30-1 to 30-3. In the apparatus disclosed inthe Patent Literature 2 described above, the DMD is used as a spatiallight modulator.

In addition, it is preferable that the incidence planes of the spatiallight modulators 30-1 to 30-3 have the same shape and size as theilluminated regions LZ1 to LZ3 which are illuminated with the coherentlight beams by the illumination device 40. This is because, in thiscase, the coherent light beams from the illumination device 40 can beused to display videos on the screens 15-1 to 15-3 with high useefficiency.

The screens 15-1 to 15-3 may be configured as transmission-type screensor as reflection-type screens. In the case where the screens 15-1 to15-3 are configured as reflection-type screens, an observer observesvideos displayed by the coherent light beams reflected by the screens15-1 to 15-3, from the same side as the projection device 20 withrespect to the screens 15-1 to 15-3. On the other hand, in the casewhere the screens 15-1 to 15-3 are configured as transmission-typescreens, the observer observes videos displayed by the coherent lightbeams passing through the screens 15-1 to 15-3, from the side oppositeto the projection device 20 with respect to the screens 15-1 to 15-3.

The coherent light beams projected on the screens 15-1 to 15-3 arediffused to be recognized as videos by an observer. At this time, thecoherent light beams projected on the screen interfere with each otherdue to the diffusion, so that speckles occur. However, in theprojection-type video display device 10 described herein, theillumination device 40 described hereinafter is configured to illuminatethe illuminated regions LZ1 to LZ3, where the spatial light modulators30-1 to 30-3 are overlapped, with the coherent light beams of whichangles are changed in time. More specifically, although the illuminationdevice 40 described hereinafter illuminates the illuminated regions LZ1to LZ3 with diffused light beams composed of the coherent light beams,the incident angle of the diffused light beams is changed in time. As aresult, the diffusion pattern of the coherent light beams on the screens15-1 to 15-3 is also changed in time, and the speckles occurring due tothe diffusion of the coherent light beams overlap in time, so that thespeckles are inconspicuous. Hereinafter, the illumination device 40 willbe described more in detail.

The illumination device 40 illustrated in FIGS. 1 and 2 includes anoptical element 50 which directs the propagation directions of thecoherent light beams as the reproduction illumination light beams(illumination light beams) La1, La2, and La3 to the correspondingilluminated regions LZ1 to LZ3 and an irradiation device 60 whichirradiates the optical element 50 with the coherent light beams as thereproduction illumination light beams La1 to La3. The optical element 50includes a hologram recording medium (light diffusion element) 55-1which can reproduce the image 5-1 of the scattering plate 6, a hologramrecording medium (light diffusion element) 55-2 which can reproduce theimage 5-2 of the scattering plate 6, and a hologram recording medium(light diffusion element) 55-3 which can reproduce the image 5-3 of thescattering plate 6. In other words, the optical element 50 includes thethree hologram recording media 55-1 to 55-3 which can reproduce theimages of the scattering plates on the corresponding illuminatedregions. In the example illustrated, the optical element 50 is composedof the hologram recording media 55-1 to 55-3.

In the example illustrated, the hologram recording media 55-1 to 55-3constituting the optical element 50 receive the correspondingreproduction illumination light beams La1 to La3 irradiated from theirradiation device 60 to diffract the reproduction illumination lightbeams with high efficiency. Particularly, the hologram recording medium55-1 diffracts the reproduction illumination light beam La1 which isincident to each position thereof, that is, a micro region which is tobe called each point thereof, so that the image 5-1 of the scatteringplate 6 can be reproduced. The same description can be made with respectto the hologram recording media 55-2 and 55-3.

On the other hand, the irradiation device 60 irradiates the opticalelement 50 with the reproduction illumination light beams La1 to La3 andallows the reproduction illumination light beams La1 to La3 to scan thecorresponding hologram recording media 55-1 to 55-3 of the opticalelement 50. Therefore, in some instant, a region of the hologramrecording medium 55-1 which is irradiated with the reproductionillumination light beam La1 by the irradiation device 60 is a portion ofthe surface of the hologram recording medium 55-1, and particularly, inthe example illustrated, the region is the micro region which is to becalled a point.

Next, the reproduction illumination light beam La1 which is irradiatedfrom the irradiation device 60 to scan the hologram recording medium55-1 is incident on each position (each point or each region (the samewill apply hereinafter)) on the hologram recording medium 55-1 with anincident angle satisfying a diffraction condition of the hologramrecording medium 55-1. Particularly, as illustrated in FIG. 2, thereproduction illumination light beam La1 which is incident from theirradiation device 60 to each position on the hologram recording medium55-1 overlappedly reproduces the image 5-1 of the scattering plate 6 onthe illuminated region LZ1. In other words, the reproductionillumination light beam La1 which is incident from the irradiationdevice 60 to each position of the hologram recording medium 55-1 isdiffused (widened) by the optical element 50 to be incident on theilluminated region LZ1.

The same description can be made with respect to the hologram recordingmedia 55-2 and 55-3. In other words, the reproduction illumination lightbeams La1 to La3 which are incident from the irradiation device 60 toeach position of each of the hologram recording media 55-1 to 55-3 allowthe images of the scattering plates corresponding to each of thehologram recording media 55-1 to 55-3 to be reproduced on thecorresponding illuminated regions. In other words, each of the spatiallight modulators 30-1 to 30-3 is illuminated with the reproductionillumination light beam which is incident from the irradiation device 60to each of the hologram recording media 55-1 to 55-3 to be diffused.

In the example illustrated, a reflection-type volume hologram using aphotopolymer is used as the hologram recording media 55-1 to 55-3 whichenable the diffraction function of the reproduction illumination lightbeams La1 to La3. Herein, as an example, a method of manufacturing thehologram recording medium 55-2 will be described. As illustrated in FIG.3, the hologram recording medium 55-2 is manufactured by using ascattered light beam from the scattering plate 6 of a real object as anobject light beam Lo. FIG. 3 illustrates a state where the hologramphotosensitive material 58 having photosensitivity which is toconstitute the hologram recording medium 55-2 is exposed by thereference light beam Lr and the object light beam Lo which are mutuallycoherent.

For example, a laser beam from the laser source which oscillates a laserbeam in a specific wavelength range is used as the reference light beamLr, and the reference light beam Lr passes through the light collectionelement 7 including lenses to be incident on the hologram photosensitivematerial 58. In the example illustrated in FIG. 3, the laser beamconstituting the reference light beam Lr is incident on the lightcollection element 7 as a parallel light flux which is parallel to anoptical axis of the light collection element 7. The reference light beamLr passes through the light collection element 7, so that the referencelight beam Lr is shaped (transformed) from the parallel light flux to aconverging light flux to be incident on the hologram photosensitivematerial 58. At this time, the focal point FP of the converging lightflux Lr is located beyond the hologram photosensitive material 58. Inother words, the hologram photosensitive material 58 is disposed betweenthe light collection element 7 and the focal point FP of the converginglight flux Lr which is condensed by the light collection element 7.

Next, the object light beam Lo as a scattered light beam from thescattering plate 6 made of, for example, an opal glass, on which theillumination light beam L is incident, is incident on the hologramphotosensitive material 58. Here, since the hologram recording medium 55which is to be manufactured is a transmission-type hologram recordingmedium, the object light beam Lo is incident from the same plane as thatof the reference light beam Lr on the hologram photosensitive material58. The object light beam Lo needs to have coherence with the referencelight beam Lr. Therefore, for example, a laser beam oscillated from thesame laser source may be divided, one of the divided beams may be usedas the reference light beam Lr described above, and the other may beused as the object light beam Lo.

In the example illustrated in FIG. 3, the parallel light flux which isparallel to the normal direction of the plate plane of the scatteringplate 6 is incident on the scattering plate 6 to be scattered, and thescattered light beam passing through the scattering plate 6 is incidentas the object light beam Lo on the hologram photosensitive material 58.According to this method, in the case where an isotropic scatteringplate which is generally available at low cost is used as the scatteringplate 6, the object light beam Lo from the scattering plate 6 can beincident on the hologram photosensitive material 58 with a substantiallyuniform light amount distribution. In addition, according to thismethod, although the light amount distribution depends on the degree ofscattering of the scattering plate 6, the reference light beam Lr iseasily incident from the entire area of the light emitting plane 6 a ofthe scattering plate 6 to each position of the hologram photosensitivematerial 58 with a substantially uniform light amount. In this case, itcan be realized that the light beam, which is incident on each positionof the hologram recording medium 55-2 obtained, reproduces the image 5-2of the scattering plate 6 with the same brightness, and the reproducedimage 5-2 of the scattering plate 6 is observed with substantiallyuniform brightness.

In this manner, if the hologram recording material 58 is exposed to thereference light beam Lr and the object light beam Lo, the interferencefringe is generated by interference between the reference light beam Lrand the object light beam Lo, and the interference fringe of the lightbeams is recorded in the hologram recording material 58 as a certainpattern (in the volume hologram, as an example, a refractive indexmodulation pattern). Next, appropriate post processes corresponding tothe type of the hologram recording material 58 are performed, so thatthe hologram recording medium 55-2 is obtained.

The hologram recording media 55-1 and 55-3 may be manufactured by usingthe same method.

FIG. 4 illustrates a diffraction function (reproduction function) of thehologram recording medium 55-2 obtained through the exposing process ofFIG. 3. As illustrated in FIG. 4, with respect to the hologram recordingmedium 55-2 formed from the hologram photosensitive material 58 of FIG.3, the light beam having the same wavelength as that of the laser beamused for the exposing process, which propagates in the reverse directionalong the optical path of the reference light beam Lr in the exposingprocess, satisfies the Bragg condition. In other words, as illustratedin FIG. 4, the diverging flux, which diverges from the standard point SPlocated with respect to the hologram recording medium 55-2 which has thesame positional relationship as the relative position (refer to FIG. 3)of the focal point FP with respect to the hologram photosensitivematerial 58 during the exposing process and has the same wavelength asthat of the reference light beam Lr during the exposing process, isdiffracted as the reproduction illumination light beam La2 by thehologram recording medium 55-2, so that the reproduced image 5-2 of thescattering plate 6 is generated at a specific position with respect tothe hologram recording medium 55-2 which has the same positionalrelationship as the relative position (refer to FIG. 3) of thescattering plate 6 with respect to the hologram photosensitive material58 during the exposing process.

At this time, the reproduction light beam (light beam obtained bydiffracting the reproduction illumination light beam La2 with thehologram recording medium 55-2) Lb2 which generates the reproduced image5-2 of the scattering plate 6 reproduces each point of the image 5-2 ofthe scattering plate 6 as a light beam which propagates in the reversedirection along the optical path of the object light beam Lo whichpropagates from the scattering plate 6 toward the hologramphotosensitive material 58 during the exposing process. In addition, asdescribed above, as illustrated in FIG. 3, the scattered light beam Lowhich emits from each position of the light emitting plane 6 a of thescattering plate 6 during the exposing process is diffused (spread) soas to be incident on the substantially entire region of the hologramphotosensitive material 58. In other words, the object light beam Lofrom the entire region of the light emitting plane 6 a of the scatteringplate 6 is incident to each position on the hologram photosensitivematerial 58, so that information of the entire light emitting plane 6 ais recorded in each position of the hologram recording medium 55-2.Therefore, each light beam constituting the diverging flux from thestandard point SP which function as the reproduction illumination lightbeam La2 illustrated in FIG. 4 is individually incident to each positionof the hologram recording medium 55-2, so that the images 5-2 of thescattering plate 6 having the same contour can be reproduced at the sameposition (illuminated region LZ2).

The same description can be made with respect to the hologram recordingmedia 55-1 and 55-3.

On the other hand, the irradiation device 60 which irradiates theoptical element 50 including the hologram recording media 55-1 to 55-3with the coherent light beams as the reproduction illumination lightbeams La1 to La3 may be configured as follows. In the exampleillustrated in FIGS. 1 and 2, the irradiation device 60 includes a lasersource 61 a which generates a coherent light beam, a light division unit62 which divides the coherent light beam from the laser source 61 a togenerate three divided light beams, optical fibers 64-1 to 64-3 whichcouple and transmit each divided light beam from the light division unit62 respectively, and a scan device 65 which changes propagationdirection of each divided light beam emitted from the optical fibers64-1 to 64-3. The light division unit 62 includes three semi-transparentmirrors to divide the coherent light beam from the laser source 61 intothree light beams. With respect to the optical fibers 64-1 to 64-3, aphotocoupling unit CI is disposed to the incidence end thereof, and aphotocoupling unit CO is disposed to the emitting end thereof. The scandevice 65 changes the propagation direction of each divided light beamin time, so that the propagation direction of each divided light beam isnot a constant direction but various directions. As a result, eachdivided light beam of which the propagation direction is changed by thescan device 65 is allowed to scan the incidence plane of thecorresponding hologram recording media 55-1 to 55-3 of the opticalelement 50, as each of the reproduction illumination light beams La1 toLa3.

Particularly, in the example illustrated in FIG. 2, the scan device 65includes three reflection devices 66-1 to 66-3 having the reflectionplane 66 a which can rotate about one axial line RA1. More specifically,each of the reflection devices 66-1 to 66-3 is configured as a mirrordevice having a mirror as the reflection plane 66 a which can rotateabout one axial line RA1. Herein, the mirror device 66-2 will bedescribed. As illustrated in FIGS. 2 and 5, the mirror device 66-2changes the orientation of the mirror 66 a to change the propagationdirection of the divided light beam from the emitting end (photocouplingunit CO) of the optical fiber 64-2. At this time, as illustrated in FIG.2, the mirror device 66-2 substantially receives the divided light beamfrom the emitting end of the optical fiber 64-2 at the standard pointSP. Therefore, the divided light beam of which the propagation directionis finally adjusted by the mirror device 66-2 can be incident on thehologram recording medium 55-2 of the optical element 50 as thereproduction illumination light beam La2 (refer to FIG. 4) which canconstitute one light beam of the diverging flux from the standard pointSP. As a result, the divided light beam from the irradiation device 60is allowed to scan the hologram recording medium 55-2, and the dividedlight beam which is incident to each position of the hologram recordingmedium 55-2 is allowed to reproduce the image 5-2 of the scatteringplate 6 having the same contour at the same position (illuminated regionLZ2).

Note that, the mirror device 66-2 illustrated in FIG. 2 is configured torotate the mirror 66 a along one axial line RA1. FIG. 5 is a perspectivediagram illustrating a configuration of the illumination device 40illustrated in FIG. 2. In the example illustrated in FIG. 5, therotation axial line RA1 of the mirror 66 a is extended in parallel tothe Y axis of the XY coordinate system defined on the plate plane of thehologram recording medium 55-2 (that is, the XY coordinate system wherethe XY plane is parallel to the plate plane of the hologram recordingmedium 55-2). Then, since the mirror 66 a rotates about the axial lineRA1 which is parallel to the Y axis of the XY coordinate system definedon the plate plane of the hologram recording medium 55-2, the incidencepoint IP of the divided light beam from the irradiation device 60 to theoptical element 50 is reciprocally moved in the direction which isparallel to the X axis of the XY coordinate system defined on the plateplane of the hologram recording medium 55-2. In other words, in theexample illustrated in FIG. 5, the irradiation device 60 irradiates theoptical element 50 with the divided light beam so that the divided lightbeam is allowed to scan the hologram recording medium 55-2 along thestraight line path.

The same description can be made with respect to the mirror devices 66-1and 66-3.

Note that, as a practical problem, there is a case where the hologramrecording material 58 is contracted during the manufacturing of thehologram recording media 55-1 to 55-3. In this case, by taking intoconsideration the shrinkage of the hologram recording material 58, it ispreferable that the recording angles of the coherent light beams, whichis irradiated on the optical element 50 by the irradiation device 60, isadjusted. The wavelength of the coherent light beam generated by thecoherent light source 61 a needs not to be strictly equal to thewavelength of the light beam used in the exposing process (recordingprocess) of FIG. 3, but the wavelengths thereof may be substantiallyequal to each other.

In addition, for the same reason, although the propagation directions ofthe light beams incident on the hologram recording media 55-1 to 55-3 ofthe optical element 50 are not taken to be strictly equal to the onelight beam constituting the diverging flux from the standard point SP,the images 5-1 to 5-3 can be reproduced in the illuminated regions LZ1to LZ3. Actually, in the example illustrated in FIGS. 2 and 5, themirror (reflection plane) 66 a of the mirror device 66-2 constitutingthe scan device 65 is necessarily shifted from the rotation axial lineRA1. Therefore, in the case where the mirror 66 a is allowed to rotateabout the rotation axial line RA1 which does not pass through thestandard point SP, the light beam incident on the hologram recordingmedium 55-2 may not be one light beam constituting the diverging fluxfrom the standard point SP. However, in a practical case, the coherentlight beam as the reproduction illumination light beam La2 from theirradiation device 60 having the illustrated configuration is allowed tosubstantially overlappedly reproduce the image 5-2 in the illuminatedregion LZ2. The same description can be made with respect to thehologram recording media 55-1 and 55-3.

Functions and Effects of Basic Embodiment

Next, the functions of the illumination device 40, the projection device20, and the projection-type video display device 10 having theconfiguration described hereinbefore will be described.

First, the irradiation device 60 irradiates the optical element 50 withthe coherent light beams as the reproduction illumination light beamsLa1 to La3 so as to allow the coherent light beams as the reproductionillumination light beams La1 to La3 to scan the corresponding hologramrecording media 55-1 to 55-3 of the optical element 50. Morespecifically, the laser source 61 a generates a coherent light beamhaving a specific wavelength which propagates in a constant direction,the light division unit 62 divides the coherent light beam into threelight beams, and each divided light beam is transmitted by thecorresponding optical fibers 64-1 to 64-3. The propagation direction ofeach divided light beam emitted from the optical fibers 64-1 to 64-3 canbe changed by the scan device 65. With respect to the hologram recordingmedium 55-1, the scan device 65 allows the divided light beam which is acoherent light beam having a specific wavelength as the reproductionillumination light beam La1 to be incident to each position of thehologram recording medium 55-1 with an incident angle satisfying theBragg Condition of the position. As a result, due to the diffraction ofthe hologram recording medium 55-1, the coherent light beam incident oneach position overlappedly reproduces the image 5-1 of the scatteringplate 6 in the illuminated region LZ1. In other words, the coherentlight beam incident from the irradiation device 60 to each position ofthe hologram recording medium 55-1 is diffused (spread) by the opticalelement 50 to be incident to the entire area of the illuminated regionLZ1. The same description can be made with respect to the hologramrecording media 55-2 and 55-3. In this manner, the irradiation device 60irradiates the illuminated regions LZ1 to LZ3 with the coherent lightbeams as the corresponding reproduction illumination light beams La1 toLa3.

As illustrated in FIG. 1, in the projection device 20, the spatial lightmodulators 30-1 to 30-3 are disposed at the positions which overlap theilluminated regions LZ1 to LZ3 of the illumination device 40. Therefore,with respect to the spatial light modulators 30-1 to 30-3, the planesthereof are illuminated by the illumination device 40, and each pixel isallowed to selectively transmit the coherent light beam, so that threevideos are formed. Each video is projected on the corresponding screens15-1 to 15-3 by the corresponding projection optical systems 25-1 to25-3. The coherent light beams projected on the screens 15-1 to 15-3 arediffused and recognized as videos by an observer. However, at this time,the coherent light beams projected on the screen interfere with eachother due to the diffusion, so that speckles occur.

However, according to the illumination device 40 of the basic embodimentdescribed herein, as described below, it is possible to very effectivelyallow the speckles to be inconspicuous. Since the speckles can beallowed to be inconspicuous according to the same principle with respectto the illuminated regions LZ1 to LZ3, the description hereinafter ismade on only the illuminated region LZ1.

The Non Patent Literature 1 described above discloses that multiplexingof parameters of polarization, phase, angle, and time and increasing ofmodes are effective to allow the speckles to be inconspicuous. Herein,the modes denote speckle patterns having no correlation therebetween.For example, in the case where the coherent light beams from a pluralityof the laser sources are projected on the same screen in differentdirections, the number of the modes is equal to the number of the lasersources exist. In addition, in the case where the coherent light beamfrom the same laser source is projected on the screen in differentdirections in a time division manner, the number of the modes is equalto the number of changing of the incident direction of the coherentlight beam within a time which may not be resolved by human eyes. Then,it is considered that, in the case where a plurality of the modes exist,the interference patterns of light beams overlap each other with nocorrelation to be averaged, so that the speckles observed withobserver's eyes are inconspicuous.

In the irradiation device 60 described above, the coherent light beam isirradiated on the optical element 50 so as to scan the hologramrecording medium 55-1. In addition, with respect to the coherent lightbeams incident from the irradiation device 60 to the positions of thehologram recording medium 55-1, although the entire region of the sameilluminated region LZ1 is illuminated with the coherent light beam, theillumination directions of the coherent light beams which areilluminated on the illuminated region LZ1 are mutually different. Then,since the position on the hologram recording medium 55-1 where thecoherent light beam is incident is changed in time, the incidentdirection of the coherent light beam incident on the illuminated regionLZ1 is also changed in time.

If the illuminated region LZ1 is considered as a standard, although thecoherent light beam is consistently incident to the positions inside theilluminated region LZ1, the incident direction is always continuouslychanged as indicated by arrow A1 in FIG. 1. As a result, the light beamconstituting each pixel of the video formed by the transmitted lightbeam of the spatial light modulator 30-1 is projected on specificposition of the screen 15-1 while the optical path is changed in time asindicated by arrow A2 in FIG. 1.

Note that, the coherent light beam is allowed to continuously scan thehologram recording medium 55-1. Accordingly, the incident direction ofthe coherent light beam incident from the irradiation device 60 to theilluminated region LZ1 is also continuously changed, and the incidentdirection of the coherent light beam incident from the projection device20 to the screen 15-1 is also continuously changed. Here, if theincident direction of the coherent light beam incident from theprojection device 20 to the screen 15-1 is changed by only a smallamount (for example, several deci-degrees), the pattern of specklesoccurring on the screen 15-1 is also greatly changed, so that specklepatterns having no correlation overlap. In addition, the frequency ofthe scan device 65 such as a MEMS mirror or a polygon mirror which isactually commercially available is typically several hundred Hz or more,and in some cases, the frequency of the scan device 65 may be severaltens of thousands of Hz.

Hereinbefore, according to the basic embodiment described above, theincident direction of the coherent light beam is changed in time at eachposition of each of the screens 15-1 to 15-3 displaying videos, and thespeed of the change thereof is such a speed that the change may not bedistinguished by human eyes, and thus, the multiplexed scatteringpatterns of the coherent light beams having no correlation are observedby human eyes. Therefore, the speckles occurring corresponding to thescattering patterns overlap to be averaged and are observed by anobserver. Therefore, with respect to the observer who observes thevideos displayed on the screens 15-1 to 15-3, the speckles are veryeffectively allowed to be inconspicuous.

Note that, with respect to the speckles observed by human in the relatedart, the speckles of the screen side may occur due to the scattering ofthe coherent light beams on the screens 15-1 to 15-3, and the specklesof the projection device side may occur due to the scattering of thecoherent light beams before projection on the screens. The specklepattern occurring at the projection device side is projected on thescreens 15-1 to 15-3 through the spatial light modulators 30-1 to 30-3,so that the speckle pattern can be recognized by the observer. However,according to the basic embodiment described above, with respect to thehologram recording medium 55-1, the coherent light beam is allowed tocontinuously scan the hologram recording medium 55-1, and the coherentlight beam which is incident to each position of the hologram recordingmedium 55-1 is illuminated on the entire region of the illuminatedregion LZ1 which the spatial light modulator 30-1 overlaps. In otherwords, the hologram recording medium 55-1 forms a new wavefrontdifferently from the existing wavefront which forms the speckle pattern,and illuminates complicatedly and uniformly the illuminated region LZ1and the screen 15-1 through the spatial light modulator 30-1. Due to theformation of the new wavefront by the hologram recording medium 55-1,the speckle pattern occurring at the projection device side may not bevisually perceived. The same description can be made with respect to thehologram recording media 55-1 and 55-3.

The Non Patent Literature 1 described above discloses a method of usinga numerical value called speckle contrast as a parameter indicating adegree of speckles occurring on the screen. When a video of a testpattern which needs to have an originally uniform luminance distributionis displayed, the video on the screen actually have a variation inluminance. The speckle contrast is a quantity defined as a valueobtained by dividing a standard deviation of the variation in luminanceby an average value of luminance. As the value of the speckle contrastis increased, the degree of occurrence of speckles on the screen isincreased, and thus, a punctate luminance irregularity pattern is moreremarkably represented to an observer.

Hereinafter, the speckle contrast on the screen 15-1 will be described.In the projection-type video display device 10 according to the basicembodiment described with reference to FIGS. 1 to 5, the specklecontrast on the screen 15-1 is measured to be 3.0% (Condition 1). Inaddition, in the case where, instead of the reflection-type volumehologram, a relief type hologram which is a computer generated hologram(CGH) having a convex-concave shape designed by using a computer so asto generate an image 5-1 of the scattering plate 6-1 when a specificreproduction illumination light beam is received is used as the opticalelement 50 described above, the speckle contrast is measured to be 3.7%(Condition 2). In the application of HDTV (high definition TV) videodisplay, although a criterion that the speckle contrast is equal to orless than 6.0% is set (for example, refer to WO 2001/081996 A1) as alevel that an observer may not almost recognize the luminanceirregularity pattern through visual observation, the basic embodimentdescribed above satisfies the criterion. In addition, actually, invisual observation, luminance irregularity (brightness irregularity) toa degree that it can be visually perceived does not occur.

On the other hand, in the case where the laser beam from the lasersource is shaped to be in the parallel light flux and is incident on thespatial light modulator 30-1, that is, in the case where the coherentlight beam from the laser source 61 a as the parallel light flux isincident on the spatial light modulator 30-1 of the projection-typevideo display device 10 illustrated in FIG. 1 without use of the scandevice 65 and the optical element 50, the speckle contrast becomes 20.7%(Condition 3). Under the condition, punctate luminance irregularitypatterns are very conspicuously observed through visual observation.

In addition, in the case where the light source 61 a is replaced with agreen LED (incoherent light source) and the light beam from the LEDlight source is incident on the spatial light modulator 30-1, that is,in the case where the incoherent light beam from the LED light source asthe parallel light flux is incident on the spatial light modulator 30-1of the projection-type video display device 10 illustrated in FIG. 1without use of the scan device 65 and the optical element 50, thespeckle contrast becomes 4.0% (Condition 4). Under the condition,luminance irregularity (brightness irregularity) to a degree that it canbe perceived through visual observation does not occur.

The results of Conditions 1 and 2 are much better than the result ofCondition 3, and the results of Conditions 1 and 2 are better than themeasurement result of Condition 4. As described above, the problem ofoccurrence of speckles is practically an intrinsic problem occurring inthe case of using a coherent light source such as a laser source, andthus, the problem needs not be considered in the case of an apparatususing an incoherent light source such as an LED. In addition, incomparison with Condition 4, in Conditions 1 and 2, the optical element50 which may cause occurrence of speckles is added. In terms of thispoint, it is considered that it is possible to sufficiently cope withthe speckle defect according to Conditions 1 and 2.

In addition, according to the basic embodiment described above, thefollowing advantages can be obtained.

According to the basic embodiment described above, the optical element50 for allowing the speckles to be inconspicuous may also function as anoptical member for shaping and adjusting the beam shape of the coherentlight beam irradiated from the irradiation device 60. Therefore, it ispossible to miniaturize and simplify the optical system.

In addition, according to the basic embodiment described above, thecoherent light beam from the laser source 61 a is used to generate thedivided light beams and the optical fibers 64-1 to 64-3 are used totransmit the divided light beams as the coherent light beams, so that itis possible to reduce a loss in light amount and reduce restriction ofarrangement of the optical system.

In addition, according to the basic embodiment described above, sincethe videos corresponding to the screens can be simultaneously displayedon the three screens 15-1 to 15-3, it is possible to increase an amountof display information in comparison with the projection-type videodisplay device displaying video on only one screen. In addition, it ispossible to perform panorama display where one video is displayed overthe three screens 15-1 to 15-3 in a seamless manner. Therefore, theprojection-type video display device according to the basic embodimentcan be used as a display having a high sense of realization.

In addition, according to the basic embodiment described above, thecoherent light beam as the reproduction illumination light beam La1which is incident to each position of the hologram recording medium 55-1is allowed to generate the image 5-1 of the scattering plate 6 at themutually same position, and the spatial light modulator 30-1 is disposedto overlap the image 5-1. The same description can be made with respectto the hologram recording media 55-2 and 55-3. Therefore, the lightbeams diffracted by the hologram recording media 55-1 to 55-3 can beused for video formation with high efficiency, so that use efficiency ofthe light from the light source 61 a is excellent.

Note that, the scan device 65 may be configured to change thepropagation directions of the divided light beams by changing thedirections of the emitting ends (photocoupling units CO) of the opticalfibers 64-1 to 64-3. In this case, the mirror devices 66-1 to 66-3 areunnecessary.

Modification of Basic Embodiment

The basic embodiment described above based on one specific exampleexemplified in FIGS. 1 to 5 can be modified in various forms.Hereinafter, modified examples will be described with reference to thedrawings. In the drawings used for the description hereinafter, thecomponents corresponding to those of the basic embodiments describedabove are denoted by the same reference numerals, and the descriptionthereof is not provided.

Projection Device

In the basic embodiment, the example where each of the spatial lightmodulators 30-1 to 30-3 is disposed at the position which overlaps thecorresponding illuminated regions LZ-1 to LZ-3 is described. However,each of the spatial light modulators 30-1 to 30-3 may not be disposed atthe position which strictly overlaps the corresponding illuminatedregions LZ-1 to LZ-3. For example, in the configuration of FIG. 1, thespatial light modulator 30-1 may be disposed to the optical element 50side rather than the illuminated region LZ-1, and the spatial lightmodulator 30-1 may be disposed to the projection optical system 25-1side rather than the illuminated region LZ-1. The same description canbe made with respect to the spatial light modulators 30-2 and 30-3. Inother words, the hologram recording media 55-1 to 55-3 and the spatiallight modulators 30-1 to 30-3 may be disposed so that the reproductionillumination light beam, which is incident to each position of each ofthe hologram recording media 55-1 to 55-3 to be diffused, overlappedlyilluminates on the corresponding spatial light modulators 30-1 to 30-3.

First Modified Example of Irradiation Device

This modified example is different from the basic embodiment describedabove in terms of only the configuration of the irradiation device 60.

FIG. 6 is a schematic diagram illustrating configurations of anillumination device, a projection device, and a projection-type videodisplay device according to a first modified example of the basicembodiment as a diagram corresponding to FIG. 1.

As illustrated in FIG. 6, the irradiation device 60 includes a lasersource 61 a which generates a coherent light beam, a light division unit62 which divides the coherent light beam from the laser source 61 togenerate three divided light beams, a scan device 65 which changespropagation direction of each divided light beam from the light divisionunit 62, converging lenses 63-1 to 63-3 which allow the divided lightbeams from the scan device 65 to converge, optical fibers 64-1 to 64-3which couple and transmit each converging divided light beam andirradiate the optical element 50 with each converging divided light beamas each of the reproduction illumination light beams La1 to La3respectively.

With respect to the optical fibers 64-1 to 64-3, a photocoupling unit CIis disposed to the incidence end thereof, and a photocoupling unit CO isdisposed to the emitting end thereof. The converging lens 63-1 allowsthe divided light beam of which the propagation direction is changed toconverge to the photocoupling unit CI of the corresponding optical fiber64-1. The converging lenses 63-2 and 63-3 have the similar function. Thescan device 65 changes the propagation direction of each divided lightbeam in time, so that the propagation direction of each divided lightbeam is not a constant direction but various directions. As a result,the divided light beams of which the propagation directions are changedby the scan device 65 as the reproduction illumination light beams La1to La3 are allowed to scan the incidence planes of the correspondinghologram recording media 55-1 to 55-3 of the optical element 50. Inother words, each of the reproduction illumination light beams La1 toLa3 constitutes the diverging flux from the emitting end of thecorresponding optical fibers 64-1 to 64-3, and each diverging flux isincident on the corresponding hologram recording media 55-1 to 55-3.

According to the modified example, it is possible to obtain the sameeffects as those of the basic embodiment described above.

Second Modified Example of Irradiation Device

This modified example is also different from the basic embodimentdescribed above in terms of only the configuration of the irradiationdevice 60.

FIG. 7 is a schematic diagram illustrating configurations of anillumination device, a projection device, and a projection-type videodisplay device according to a second modified example of the basicembodiment as a diagram corresponding to FIG. 1.

As illustrated in FIG. 7, the irradiation device 60 includes a lasersource 61 a which generates a coherent light beam, a light division unit62 which divides the coherent light beam from the laser source 61 a togenerate three divided light beams, mirror optical systems 68-1 to 68-3which transmit each divided light beam from the light division unit 62respectively, and a scan device 65 which changes the propagationdirection of each divided light beam incident from the mirror opticalsystems 68-1 to 68-3.

The mirror optical systems 68-1 to 68-3 are configured with a pluralityof mirrors so that the incident light beams are transmitted due toreflection of the mirrors. The scan device 65 changes the propagationdirection of each divided light beam in time, so that the propagationdirection of each divided light beam is not a constant direction butvarious directions. As a result, each divided light beam of which thepropagation direction is changed by the scan device 65 as each of thereproduction illumination light beams La1 to La3 is allowed to scan theincidence plane of the corresponding hologram recording media 55-1 to55-3 of the optical element 50.

According to the modified example, it is possible to obtain the sameeffects as those of the basic embodiment described above.

Third Modified Example of Irradiation Device

This modified example is also different from the basic embodimentdescribed above in terms of only the configuration of the irradiationdevice 60.

FIG. 8 is a schematic diagram illustrating configurations of anillumination device, a projection device, and a projection-type videodisplay device according to a third modified example of the basicembodiment as a diagram corresponding to FIG. 1.

As illustrated in FIG. 8, the irradiation device 60 includes a lasersource 61 a which generates a coherent light beam, a scan device 65which changes a propagation direction of the coherent light beam fromthe laser source 61 a, a collimation optical system 69 which collimatesthe coherent light beam from the scan device 65 as a parallel lightbeam, a light division unit 62 which divides the collimated coherentlight beam as a parallel light beam into three divided light beams, andmirror optical systems 68-1 to 68-3 which transmit each divided lightbeam from the light division unit 62 and irradiate the optical element50 with each divided light beam as each of the reproduction illuminationlight beams La1 to La3 respectively.

The scan device 65 changes the propagation direction of the coherentlight beam in time, so that the propagation direction of the coherentlight beam is not a constant direction but various directions. Thecoherent light beam of which the propagation direction is changed intime is collimated, and the position where the collimated light beam isincident on a semi-transparent mirror constituting the light divisionunit 62 is changed in time. Therefore, the positions where the threedivided light beams divided by the light division unit 62 are incidenton the mirror optical systems 68-1 to 68-3 are changed in time. As aresult, each divided light beam from the mirror optical systems 68-1 to68-3 is allowed to scan the incidence plane of the correspondinghologram recording media 55-1 to 55-3 of the optical element 50 as eachof the reproduction illumination light beams La1 to La3. In other words,each of the reproduction illumination light beams La1 to La3 constitutesthe parallel light flux, and each parallel light flux is incident on thecorresponding hologram recording media.

According to the modified example, it is possible to obtain the sameeffects as those of the basic embodiment described above.

Spatial Light Modulator, Projection Optical System, and Screen

According to the embodiments described above, the speckles areeffectively allowed to be inconspicuous. However, the functions andeffects are obtained mainly from the illumination device 40. Then, inthe case where the illumination device 40 is configured as a combinationof various existing spatial light modulators, projection opticalsystems, screens, and the like, the speckles are effectively allowed tobe inconspicuous. Due to this point, the spatial light modulators, theprojection optical systems, and the screens are not limited to theexemplified ones, but various existing members, parts, apparatuses, andthe like may be used.

Projection-Type Video Display Device

In addition, although the example where the hologram recording media55-1 to 55-3 are manufactured by using the planar scattering plate 6having a shape corresponding to the incidence planes of the spatiallight modulators 30-1 to 30-3 and by an interference exposing method isillustrated, the present invention is not limited thereto. The hologramrecording media 55-1 to 55-3 may be manufactured by using a scatteringplate having some pattern and by an interference exposing method. Inthis case, the image of the scattering plate having some pattern isreproduced by the hologram recording media 55-1 to 55-3. In other words,the optical element 50 (hologram recording media 55-1 to 55-3)illuminates the illuminated regions LZ1 to LZ3 having some patterns. Inthe case where the optical element 50 is used, the spatial lightmodulators 30-1 to 30-3 and the projection optical systems 25-1 to 25-3may be not provided from the basic embodiment described above, and thescreens 15-1 to 15-3 are disposed at the positions which overlap theilluminated regions LZ1 to LZ3, so that some patterns recorded in thehologram recording media 55-1 to 55-3 can be displayed on the screens15-1 to 15-3. In this display device, the irradiation device 60irradiates the optical element 50 with the coherent light beams so thatthe coherent light beams are allowed to scan the hologram recordingmedia 55-1 to 55-3, so that it is possible to allow the speckles to beinconspicuous on the screens 15-1 to 15-3.

Irradiation Device

In the embodiment described above, an example where the irradiationdevice 60 includes the laser source 61 a and the scan device 65 isillustrated. Although the scan device 65 which is configured withone-axis-rotation type mirror devices 66-1 to 66-3 which change thepropagation direction of the coherent light beam by reflection isexemplified, the scan device 65 is not limited thereto. Herein, themirror device 66-2 will be described. As illustrated in FIG. 9, the scandevice 65 may be configured so that the mirror (reflection plane 66 a)of the mirror device 66-2 can rotate about the first rotation axial lineRA1 as well as about the second rotation axial line RA2 intersecting thefirst rotation axial line RA1. In the example illustrated in FIG. 9, thesecond rotation axial line RA2 of the mirror 66 a is perpendicular tothe first rotation axial line RA1 which is extended in parallel to the Yaxis of the XY coordinate system defined on the plate plane of thehologram recording medium 55-2. Then, since the mirror 66 a can rotateabout both of the first axial line RA1 and the second axial line RA2,the incidence point IP of the coherent light beam from the irradiationdevice 60 incident on the optical element 50 can be moved on the plateplane of the hologram recording medium 55-2 in two-dimensionaldirections. Therefore, as an example, as illustrated in FIG. 9, theincidence point IP of the coherent light beam incident on the opticalelement 50 may also be configured to be moved along a circumference. Themirror devices 66-1 and 66-3 may be configured in a similar manner.

In addition, the scan device 65 may include four or more mirror devices.In this case, for example, although the mirror 66 a of the mirror device66-2 can rotate about only a single axial line, the incidence point IPof the coherent light beam from the irradiation device 60 incident onthe optical element 50 can be moved on the plate plane of the hologramrecording medium 55-2 in two-dimensional directions by other mirrordevices. The mirror devices 66-1 and 66-3 may be configured in a similarmanner.

In addition, as a specific example of the mirror devices 66-1 to 66-3included in the scan device 65, there are a MEMS mirror, a polygonalmirror, and the like.

In addition, the scan device 65 may be configured to include a deviceexcept a reflection device (for example, the mirror devices 66-1 to 66-3described above) which changes the propagation direction of the coherentlight beam through reflection. For example, the scan device 65 mayinclude a refraction prism or lens or the like.

Essentially, the scan device 65 is not a necessary component. The lightsource 61 a of the irradiation device 60 is configured so that the lightsource can be displaced (moved, oscillated, and rotated) with respect tothe optical element 50 and so that the reproduction illumination lightbeams La1 to La3 based on the coherent light beams irradiated from thelight source 61 a are allowed to scan the corresponding hologramrecording media 55-1 to 55-3 according to the displacement of the lightsource 61 a with respect to the optical element.

In addition, although the description hereinbefore is made under thepresumption that the light source 61 a of the irradiation device 60oscillates a laser beam which is shaped as a linear light beam, thepreset invention is not limited thereto. Particularly, in the embodimentdescribed above, the coherent light beam as the reproductionillumination light beam La1 irradiated to each position of the opticalelement 50 is shaped by the optical element 50 as a light flux which isincident on the entire region of the illuminated region LZ1. The samedescription can be made with respect to the reproduction illuminationlight beams La2 and La3. Therefore, although the coherent light beams asthe reproduction illumination light beams La1 to La3 irradiated from thelight source 61 a of the irradiation device 60 to the optical element 50are not accurately shaped, no problem occurs. For this reason, thecoherent light beam generated from the light source 61 a may be adiverging light beam. In addition, the shape of cross section of thecoherent light beam generated from the light source 61 a may an ellipseor the like instead of a circle. In addition, the transverse mode of thecoherent light beam generated from the light source 61 a may be amulti-mode.

In addition, in the case where the light source 61 a generates thediverging flux, when the coherent light beams as the reproductionillumination light beams La1 to La3 are incident on the hologramrecording media 55-1 to 55-3 of the optical element 50, each of thelight beams is incident on not a spot but a region having somewhat area.In this case, the light beams which are diffracted by the hologramrecording media 55-1 to 55-3 to be incident to the positions of thecorresponding illuminated regions LZ1 to LZ3 are multiplexed in terms ofangle. In other words, in each instant, the coherent light beams areincident from the directions of certain angle ranges to the positions ofthe illuminated regions LZ1 to LZ3. Due to the multiplexing in terms ofangle, it is possible to more effectively allow the speckles to beinconspicuous.

In addition, in the embodiment described above, although the examplewhere the irradiation device 60 allows the coherent light beam to beincident on the optical element 50 so as to trace the optical path ofthe one light beam constituting the diverging flux is described, thepresent invention is not limited thereto. For example, in the aboveembodiment, as illustrated in FIG. 10, the scan device 65 may beconfigured to further include a collection lens (parallel lightgeneration unit) 67 disposed at the lower stream side of the mirrordevice 66-2 along the optical path of the coherent light beam. In thiscase, the light beam from the mirror device 66-2, which propagates alongthe optical path of the light beam constituting the diverging flux, isallowed by the collection lens 67 to become the light beam whichpropagates in a certain direction. In other words, the irradiationdevice 60 allows the coherent light beam as the reproductionillumination light beam La1 to be incident on the optical element 50 soas to trace the optical path of the light beam constituting the parallellight flux. In this example, in the exposing process during themanufacturing of the hologram recording medium 55-2, instead of theconverging light flux described above, the parallel light flux is usedas the reference light beam Lr. The hologram recording medium 55-2 canbe more simply manufactured and replicated.

Similarly, with respect to the mirror devices 66-1 and 66-3, thecollection lens 67 may be disposed at the downstream side.

Similarly, in the second modified example of the irradiation deviceillustrated in FIG. 7, the scan device 65 may further include collectionlenses which are disposed at the downstream sides of the mirror devices66-1 to 66-3 along the optical paths of the coherent light beams.

In the embodiment described above, the example where the irradiationdevice 60 includes only one laser source 61 a is described. However, thepresent invention is not limited thereto. For example, the irradiationdevice 60 may include a plurality of the light sources which oscillatelight beams having the same wavelength range. In this case, theillumination device 40 can illuminate the illuminated regions LZ1 to LZ3more brightly. In addition, the coherent light beams from differentlaser sources have no coherency. Therefore, the multiplexing of thescattering patterns further progresses, so that it is possible to allowthe speckles to be more inconspicuous.

In addition, the irradiation device 60 may include a plurality of thelight sources which generate the coherent light beams having differentwavelength ranges. According to this example, a color which is hard todisplay by using a single laser beam is generated through additive colormixing, and the illuminated regions LZ1 to LZ3 can be illuminated withthe generated color. In addition, in this case, in the projection device20 or the transmission-type video display device 10, in the case wherethe spatial light modulators 30-1 to 30-3 include, for example, colorfilters and are capable of forming modulation image with respect to eachcoherent light beam having each wavelength range, the video can bedisplayed in a plurality of colors. In addition, although the spatiallight modulators 30-1 to 30-3 do not includes color filters, in the casewhere the irradiation device 60 irradiates the coherent light beamhaving each wavelength range in a time division manner and the spatiallight modulators 30-1 to 30-3 operate in a time division manner so as toform modulation image corresponding to the irradiated coherent lightbeam having the wavelength range, the video can be displayed in aplurality of colors. Particularly, in the projection device 20 or thetransmission-type video display device 10, in the case where theirradiation device 60 includes a light source which generates thecoherent light beam having a wavelength range corresponding to redlight, a light source which generates the coherent light beam having awavelength range corresponding to green light, and a light source whichgenerates the coherent light beam having a wavelength rangecorresponding to blue light, the video can be displayed in full colors.

In addition, the hologram recording media 55-1 to 55-3 included in theoptical element 50 have wavelength selectivity. Therefore, in the casewhere the irradiation device 60 includes light sources having differentwavelength ranges, the hologram recording media 55-1 to 55-3 may beconfigured to include hologram components corresponding to thewavelength ranges of the coherent light beams generated from the lightsources in a laminated state. The hologram components for the coherentlight beams having the wavelength ranges may be manufactured by usingthe coherent light beams having the corresponding wavelength ranges asthe light beams for exposing (reference light beam Lr and object lightbeam Lo), for example, in the method described above with reference toFIGS. 3 and 4. In addition, instead of manufacturing the hologramrecording media 55-1 to 55-3 by laminating the hologram components forthe wavelength ranges, the hologram photosensitive material 58 issimultaneously exposed with the object light beam Lo and the referencelight beam Lr which are obtained from the coherent light beams havingthe wavelength ranges, and a plurality of light beams having wavelengthranges are diffracted by single hologram recording media 55-1 to 55-3.

Optical Element

In the embodiment described above, although the example where theoptical element 50 is configured with the reflection-type volumehologram recording media 55-1 to 55-3 using photopolymer is described,the present invention is not limited thereto. In addition, the opticalelement 50 may include a type of a volume hologram recording mediumwhere recording is performed by using a photosensitive medium includinga silver halide material. In addition, the optical element 50 mayinclude a reflection-type volume hologram recording medium, and theoptical element 50 may include a relief type (emboss type) hologramrecording medium.

With respect to the relief type (emboss type) hologram recording medium,hologram interference fringe is recorded by using a convex-concavestructure of a surface thereof. However, in the case of the relief typehologram recording medium, since scattering due to the convex-concavestructure of the surface may also cause occurrence of new speckles, thevolume hologram recording medium is preferred. In the case of the volumehologram recording medium, hologram interference fringe is recorded byusing a refractive index modulation pattern (refractive indexdistribution) of an inner portion of the medium, there is no influenceof the scattering due to the convex-concave structure of the surface.

However, even in the case of the volume hologram recording medium, ifrecording is performed by using a photosensitive medium including asilver halide material, scattering due to silver halide particles mayalso cause occurrence of speckles. Therefore, as the hologram recordingmedia 55-1 to 55-3, the volume hologram recording medium using aphotopolymer is preferred.

The reflection-type hologram recording medium is higher than thetransmission-type hologram recording medium in terms of the wavelengthselectivity. In other words, in the reflection-type hologram recordingmedium, although interference fringes corresponding to a differentwavelength are laminated, a coherent light beam having a desiredwavelength can be diffracted by using only a desired layer. In addition,in terms of removing the influence of the zeroth-order light beam, thereflection-type hologram recording medium is excellent.

On the other hand, although the transmission-type hologram recordingmedium has a wide diffractable spectrum range and a high degree ofallowance of the laser source, if interference fringes corresponding todifferent wavelengths are laminated, layers other than a desired layeralso diffract the coherent light beam having a desired wavelength.Therefore, in general, it is difficult to configure thetransmission-type hologram recording medium in a lamination structure.

In addition, in the exposing process illustrated in FIG. 3, although aso-called Fresnel type hologram recording medium is manufactured, aFourier transform type hologram recording medium which can be obtainedthrough recording using lenses may be manufactured. However, in the caseof using a Fourier transform type hologram recording medium, the lensescan be used even during the reproduction.

In addition, a striped pattern (refractive index modulation pattern orconvex-concave pattern) which is to be formed on the hologram recordingmedia 55-1 to 55-3 may be designed by using a computer based onwavelengths or incident directions of predetermined reproductionillumination light beams La1 to La3, shapes or positions ofto-be-reproduced images, and the like without use of the actual objectlight beam Lo and the reference light beam Lr. The hologram recordingmedia 55-1 to 55-3 obtained in this manner are called computer generatedhologram recording media. In addition, similarly to the modified exampledescribed above, in the case where a plurality of the coherent lightbeams having mutually different wavelength ranges are irradiated fromthe irradiation device 60, the hologram recording media 55-1 to 55-3 asthe computer generated hologram recording media may be configured so asto be partitioned two-dimensionally into a plurality of regions disposedcorresponding to the coherent light beams having the wavelength ranges,and the coherent light beams having the wavelength ranges are diffractedby the corresponding regions to reproduce images.

In addition, in the embodiment described above, although the examplewhere the optical element 50 includes the hologram recording media 55-1to 55-3 which spread the coherent light beams irradiated to thepositions thereof and illuminate the corresponding illuminated regionsLZ1 to LZ3 with the spread coherent light beams is described, thepresent invention is not limited thereto. Instead of the hologramrecording media 55-1 to 55-3 or in addition to the hologram recordingmedia 55-1 to 55-3, the optical element 50 may include a plurality oflens arrays (light diffusion elements) as optical components capable ofchanging the propagation direction of the incident light beam anddiffusing the light beam and illuminating the corresponding illuminatedregion among a plurality of the illuminated regions LZ1 to LZ3. As aspecific example of the lens array, a total reflection-type orrefraction-type Fresnel lens added with a diffusion function, a fly-eyelens, or the like may be exemplified. In the illumination device 40, theirradiation device 60 and the optical element 50 may also configured sothat the irradiation device 60 allows the coherent light beam to scaneach lens array, irradiates the optical element 50 with the coherentlight beam and so that the propagation direction of the coherent lightbeam incident from the irradiation device 60 to each position of theoptical element 50 is changed by the corresponding lens array to beilluminated on the corresponding illuminated regions LZ1 to LZ3.Therefore, it is possible to effectively allow the speckles to beinconspicuous.

Illuminating Method

In the embodiment described above, as an example, the irradiation device60 is configured so as to allow the coherent light beams to scan theoptical element 50 in one-dimensional direction, and the hologramrecording media 55-1 to 55-3 (or lens arrays) of the optical element 50are configured so as to diffuse (spread, diverge) the coherent lightbeams irradiated to the positions in two-dimensional directions, so thatthe illumination device 40 illuminates the illuminated regions LZ1 toLZ3 in a two-dimensional manner. However, as described above, thepresent invention is not limited to. For example, the irradiation device60 may be configured so as to allow the coherent light beams to scan theoptical element 50 in two-dimensional directions, and the hologramrecording media 55-1 to 55-3 (or lens arrays) of the optical element 50may be configured so as to diffuse (spread, diverge) the coherent lightbeams irradiated to the positions in two-dimensional directions, so thatthe illumination device 40 illuminates the illuminated regions LZ1 toLZ3 in a two-dimensional manner (described above with reference to FIG.9).

Combination of Modified Examples

In addition, although several modified examples of the basic embodimentsare described hereinbefore, it is obvious that a combination of aplurality of the modified examples is available.

Number of Screens

In the description hereinbefore, although the example where theprojection-type video display device 10 includes the three screens 15-1to 15-3 is described, the projection-type video display device 10 mayinclude two screens or four or more screens. In these cases, theprojection device may include the hologram recording media, the spatiallight modulators, and the projection optical systems, of which therespective number is equal to the number of screens. The images of thescattering plates are recorded in the hologram recording media. Inaddition, the projection device may include the irradiation device whichirradiates the divided light beams of which the number is equal to thenumber of screens and allows each divided light beam as eachreproduction illumination light beam to scan the corresponding hologramrecording media.

1. An illumination device illuminating a plurality of illuminatedregions, comprising: an optical element comprising a plurality of lightdiffusion elements capable of diffusing light; and an irradiation deviceconfigured to irradiate the optical element with a plurality ofillumination light beams, each illumination light beam scanning thecorresponding light diffusion element, wherein the illumination lightbeam, which is incident to each position of each light diffusion elementto be diffused, overlappedly illuminates on corresponding illuminatedregion, and wherein the irradiation device comprises: a light sourceconfigured to generate a coherent light beam; a light division unitconfigured to divide the coherent light beam from the light source togenerate a plurality of divided light beams; and a scan deviceconfigured to change propagation direction of each divided light beamfrom the light division unit and allow each divided light beam as eachillumination light beam to scan the corresponding light diffusionelement.
 2. An illumination device illuminating a plurality ofilluminated regions, comprising: an optical element comprising aplurality of light diffusion elements capable of diffusing light; and anirradiation device configured to irradiate the optical element with aplurality of illumination light beams, each illumination light beamscanning the corresponding light diffusion element, wherein theillumination light beam, which is incident to each position of eachlight diffusion element to be diffused, overlappedly illuminates oncorresponding illuminated region, and wherein the irradiation devicecomprises: a light source configured to generate a coherent light beam;a scan device configured to change a propagation direction of thecoherent light beam from the light source; and a light division unitconfigured to divide the coherent light beam from the scan device togenerate a plurality of divided light beams, wherein the scan deviceallows each illumination light beam to scan the corresponding lightdiffusion element.
 3. The illumination device according to claim 2,further comprising mirror optical systems, each mirror optical systemtransmitting each divided light beam from the light division unit andirradiating the optical element with each divided light beam as eachillumination light beam.